Insulating Gap Between Exterior and Interior Foam
Hi all, I have an insulation question. My house was planned as a slab inside 5′ frost walls (zone 6 southern coastal maine). After walls were poured the builder at the time and I decided to change it to a crawlspace with a framed floor instead, due to a couple of problems that came up. So the architect designed a floor framed on 2×12 PT ledgers attached to the inside top foot of the frost wall with wedge anchors, so the subfloor sits at the level the slab was supposed to be. I insulated the crawlspace with 3 1/2″ XPS inside the walls from top of footing up to about an inch below where the ledger would go, taped seams, and before that Drylok’d interior and exterior everywhere there wasn’t going to be foam board. Also have an exterior dimple mat on lower 4′ of walls. The house will also have continuous exterior insulation, mostly as 3 1/2″ EPS EIFS system for siding, with some areas having a band of faux stone at the bottom with 3″ graphite EPS under it. Grade is at about 6-10″ below top of frost wall, depending if it’s near garage doors or other parts of the house. So that leaves me with several inches of space to figure out how to insulate, between the bottom of exterior foam/siding and the top of the XPS on the interior. My 2×12 ledger area therefore has the top part of it insulated on the exterior with foam board, but the lower part of it has just cold concrete behind it. I put foam sill sealer behind the PT ledgers so they aren’t touching concrete. But now I am not sure if I should closed cell spray foam the inside of crawlspace walls from the top of the interior XPS up to the bottom of the subfloor, encapsulating the ledger? This will create a foam sandwich for the top half of my 2×12 ledger. It can’t dry to the exterior through the concrete anyway but it would eliminate it being able to dry to the interior. Or use rockwool insulation instead? This would allow it to dry but also allow interior air to reach the cold concrete wall on the bottom half of the ledger. With none of the exterior insulation up yet I’ve already witnessed tons of condensation along the ledger and joist hangers just from hot humid days. So I’m leaning towards the spray foam. Thoughts?
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